1. Field of the Invention
This invention relates generally to apparatus for closed die metal forging and, more particularly, to an accumulator system for controlling the clamping pressure on the dies during the forging operation.
2. Description of the Prior Art
In closed die forging, dies on bolster and ram elements of a forging machine are clamped together by fluid pressure as a punch and an anvil on the ram and the bolster first upset and then extrude a metal blank or slug within a closed die cavity defined between the dies. To minimize noise and impact, it is desirable that the fluid pressure be low when the dies make initial closing contact. However, because of the high separating forces on the dies characteristic of upsetting and extrusion, the fluid pressure must very quickly achieve a correspondingly high magnitude. Typically, clamping force on the dies is developed in variable volume oil chamber behind the dies and a conventional single piston air/oil accumulator is connected to the oil chambers such that clamping pressure increases as a function of ram travel. In such systems, the limited available ram travel after the dies engage renders it is difficult to achieve both quiet die closing and acceptably high ultimate oil pressure. That is, if the initial oil pressure is low for quietness the ultimate pressure will be insufficient for upsetting/extrusion and if the ultimate pressure is sufficient for upsetting/extrusion the initial pressure will be too high for quietness. An accumulator system according to this invention represents an improvement over the aforesaid systems in that it incorporates simple and economical structure whereby quiet die engagement and high ultimate oil pressure for clamping the dies together are both readily achieved.